Uplink power control for distributed wireless communication

ABSTRACT

A method and apparatus for power control for distributed wireless communication is disclosed including one or more power control loops associated with a wireless transmit/receive unit (WTRU). Each power control loop may include open loop power control or closed loop power control. A multi-phase power control method is also disclosed with each phase representing a different time interval and a WTRU sends transmissions at different power levels to different set of node-Bs or relay stations during different phases to optimize communications.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 61/119,637 filed on Dec. 3, 2008, which is incorporated by referenceas if fully set forth herein.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

In orthogonal frequency division multiplexing (OFDM), single-carrierfrequency-division multiple access (SC-FDMA), Long Term Evolution (LTE),802.16, code division multiple access (CDMA), or other wireless networktechnologies transmissions from different cells may share the sameuplink (UL) resources. In a single cell, different data streams thatbelong to the same wireless transmit/receive unit (WTRU) or differentWTRUs may share the same resources. Because of resource sharing, it maybe desirable to adjust the WTRU's total transmission power in order toachieve a desired quality of service (QoS), acceptable intra-cell andinter-cell interference level, improved cell-edge performance, extendedcell coverage, or the like. Precise power control may also be desirablein systems using multi-user multiple in/multiple out (MU-MIMO)transmissions.

Many wireless networks support open loop and closed loop power controlschemes. Open loop power control may be performed to fully or partiallycompensate for short-term and/or long-term channel variations that aredetermined in the WTRU based on downlink channel estimations, channelstate information, channel noise modeling, or the like. For closed looppower control, a power control command provided by a base station issignaled to the WTRU for correcting errors occurring in the open looppower control. The correction of the transmit power in the closed loopmay be either accumulated or absolute.

LTE, 802.16, MIMO, or CDMA based networks may also be setup asdistributed communications, systems, or networks where one or more WTRUscommunicate concurrently with at least two or more base stations usingmultiple independent, and sometimes simultaneous, communications.Moreover, distributed communications may include relay stations (RSs). ARS, in general, is a device that relays or repeats communication backand forth between one or more WTRUs and at least one base station. In adistributed communication one or more WTRUs may simultaneouslycommunicate with two or more relay stations and two or more basestations, as desired.

A WTRU may receive a power control command from each RS or base stationit communicates with in a distributed network. This creates a problemsince the power control commands are uncoordinated and sometimesconflicting with each RS or base station trying to meet it's own signalto interference plus noise ratio (SINR) level causing a less than idealoverall system performance. A need exists in distributed wirelesscommunications for power control to reduce power consumption of a WTRU,mitigate intra-cell and inter-cell interference, and maintain a desiredQoS, SINR, or block error rate (BLER).

SUMMARY

A method and apparatus for power control for distributed wirelesscommunication is disclosed comprising one or more power control loopsassociated with a WTRU. Each power control loop may include open looppower control or closed loop power control. A multi-phase power controlmethod is also disclosed with each phase representing a different timeinterval and a WTRU sends transmissions at different power levels todifferent set of node-Bs or relay stations during different phases tooptimize communications.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows an example wireless communication system including wirelesstransmit/receive units (WTRUs), evolved node-Bs, gateways, and relaystations (RSs);

FIG. 2 is a functional block diagram of a WTRU, an evolved node-B, andRS of FIG. 1;

FIG. 3( a) is an example of a WTRU receiving a transmit power command(TPC) command from a RS;

FIG. 3( b) is an example of a WTRU receiving multiple TPC commands frommultiple RSs;

FIG. 4 is an example of a WTRU response to multiple TPC commands from NRSs;

FIGS. 5( a) and 5(b) are examples of coordinated power control;

FIGS. 6( a) and 6(b) are examples of uplink power control for anopportunistic cooperation configuration in a two-phase power controlsystem;

FIGS. 7( a) and 7(b) are examples of uplink power control for anopportunistic cooperation configuration in a two-phase power controlsystem;

FIGS. 8( a) and 8(b) shows an example of power control for a strongcooperation configuration in a two-phase power control system;

FIG. 8( c) shows an example of a response to multiple TPC commands froma eNB and RS;

FIG. 9 shows an example of multi-loop power control in a MIMO basednetwork;

FIG. 10 is a flow diagram of a process in accordance with the presentdescription; and

FIG. 11 is a flow diagram of another process in accordance with thepresent description.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment. In the forthcoming description, even though an evolvednode-B (eNB) may be used throughout the present description, it may beconfigured or adapted to networks having legacy base stations. Moreover,although some of the examples given below are for uplink power controlthe present description may also be configured or adapted for downlinkpower control.

FIG. 1 shows a Long Term Evolution (LTE) wireless communicationsystem/access network 100 that includes an Evolved-Universal TerrestrialRadio Access Network (E-UTRAN) 105. The E-UTRAN 105 includes a WTRU 110,at least two relay stations (RSs) 115 ₁-115 ₂, and several eNBs 120₁-120 ₃. WTRU 110 is in communication with one or more eNBs 120 ₁-120 ₃and/or relay stations 115 ₁-115 ₂. The eNBs 120 ₁-120 ₃ interface witheach other using an X2 interface. Each of the eNBs 120 ₁-120 ₃ interfacewith a Mobility Management Entity (MME)/Serving GateWay (S-GW) 130 ₁ or130 ₂ through an S1 interface. Although a single WTRU 110 and three eNBs120 ₁-120 ₃ are shown in FIG. 1, it should be apparent that anycombination of wireless and wired devices may be included in wirelesscommunication system/access network 100.

FIG. 2 is a block diagram of an LTE wireless communication system 200including WTRU 110, RS 115, eNB 120, and MME/S-GW 130. As shown in FIG.2, WTRU 110, RS 115, eNB 120 and MME/S-GW 130 are configured to performa method of uplink power control for distributed wirelesscommunications. Although FIGS. 1 and 2 are examples of LTE networks,similar networks configured for CDMA, 802.16, or High Speed PacketAccess (HSPA) communications is envisioned and applicable to theexamples and embodiments described herein.

In addition to the components that may be found in a typical WTRU, WTRU110 includes a processor 216 with an optional linked memory 222, atleast one transceiver 214, an optional battery 220, and an antenna 218.The processor 216 is configured to perform a method of uplink powercontrol for distributed wireless communication. Transceiver 214 is incommunication with processor 216 and antenna 218 to facilitate thetransmission and reception of wireless communications. In case a battery220 is used in the WTRU 110, it powers transceiver 214 and processor216.

In addition to the components that may be found in a typical RS, RS 115includes a processor 226 with an optional linked memory 227,transceivers 224, and antennas 225. Processor 226 is configured toperform a method of uplink power control for distributed wirelesscommunication. Transceivers 224 are in communication with processor 226and antennas 225 to facilitate the transmission and reception ofwireless communications.

In addition to the components that may be found in a typical eNB, eNB120 includes a processor 217 with an optional linked memory 215,transceivers 219, and antennas 221. Processor 217 is configured toperform a method of uplink power control for distributed wirelesscommunication. Transceivers 219 are in communication with processor 217and antennas 221 to facilitate the transmission and reception ofwireless communications. The eNB 120 is connected to the MobilityManagement Entity/Serving GateWay (MME/S-GW) 130 which includes aprocessor 233 with an optional linked memory 234.

Still referring to FIG. 2, WTRU 110 and eNB 120 may each be configuredto perform multi-phase power control in a distributed MIMO system. Eachphase in multi-phase power control may be a time interval where WTRU 110communicates with eNB 120 or both eNB 120 and RS 115. For example, in afirst phase time interval WTRU 110 may communicate with both eNB 120 andRS 115, and to eNB 120 in a second phase time interval. For each phasean independent power control loop, either open or closed loop, may beprovided. Although a two phase configuration is given, N RSs 115 may beprovided between WTRU 110 and eNB 120 to have a multi-phase powercontrol system of N+1 phases in FIG. 2 and other examples set forthherein. With N+1 phases, each phase may be the same or different timeinterval.

Moreover, in a distributed communication network power control for WTRU110 may or may not depend on the specific network topology. However, thedelivery of power control commands for closed loop power control, andthe forwarding of both types of power control may be dependent on thetopology of wireless communication system/access network 100.

A power control loop may be an apparatus or process for setting andadjusting a transmitter's transmit power during the transmission timethat may be associated with a particular type of transmission. Thesetting and adjustment may be based on measurements performed at thetransmitter in open loop or eNB/relay station feedback via commands inclosed loop, or both. Open loop power control may be used to compensatefor long term channel variations due to path loss, shadowing, or thelike, between WTRU 110 and eNB 120 or RS 115. Closed loop power controlmay be used to correct errors from open loop power control, compensatefor short-term fading, or mitigate inter-cell-interference.

Since power control loops between a transmitter and receiver may beindependent, power control for closed loop may not always be combinable.Rather, each power control loop may operate independently to track anddetermine its necessary transmit power. At the time of transmission,WTRU 110 may select the power setting as determined by the appropriatepower control loop.

WTRU 110 using open loop power control may base its transmission poweron a long-term averaged downlink pathloss estimate between itself andeNB 120 and/or RS 115. For closed loop power control WTRU 110 may use apower control command provided by a controlling node such as a RS, aneNB, or joint eNB and RS to correct errors. Types of errors may includemeasurement errors, power amplification errors, or the like.

Moreover, the transmission of a power control command may identify whichpower control loop WTRU 110 should be associated with in the network. Ina first option, explicit signaling may be used to identify the powercontrol loop. A pre-negotiating of the nature of each power control loopvia higher-layer signaling may also be performed. However, this mayrequire additional bandwidth to transmit each power control commandcomprising of a power control command and a power control loopidentifier.

In a second option, implicit signaling based on timing may be used toidentify a power control loop. A power control command may be associatedwith a particular power control loop based on the timing of itstransmission. For example, if a power control command may be sentfollowing a fixed amount of time after a particular data transmission,this may allow association of the message with the loop that governedthat particular data transmission. This power control command may beprovided by a eNB 120 ₁ acting as a master controlling node of multipleeNBs 120 ₂-120 ₃ or RSs 115 ₁-115 ₂ in a particular loop, such as byhigher layer signaling or one of the multiple eNBs or RSs aftercommunication with multiple eNBs or RSs. The timing may be implied bythe choice of the sub-frame to be associated with eNB 120 or RS 115,which may be referred to as a zone.

In another option for associating a power control command with a powerloop, implicit signaling may be based on a terminal identifier (ID), inorder to identify a power control loop. In the case where power controlloops are identified with unique combination of receiving eNBs 120 ₁-120₃ or RSs 115 ₁-115 ₂, simultaneous transmission of commands by multipleeNBs or RSs may be used to associate the command with a particular powercontrol loop. The eNB 120 or RS 115 may be configured to associate apower control command with a specific control channel or signature.Alternatively, hybrid implicit signaling may be implemented where acombination of the above options may be used to identify a power controlloop.

The eNB 120 or RS 115 may also be configured to simultaneously transmitpower control commands, or to combine multiple and potentially differentpower control commands. Alternatively multiple eNBs or RSs may beconfigured to coordinate power control commands, wherein one combinedpower control command may be sent to WTRU 110.

For open loop power control, there may be one eNB or RS associated withone loop or multiple eNBs or RSs associated with one loop in adistributed communication network. For the case of multiple eNBs or RSs,an appropriate value to compensate the long-term variation between WTRU110 and several eNBs or RSs may be desired.

In a distributed communication network, multiple eNBs or RSs may each beconfigured to jointly decode information after partial individualreception if the signal quality at any one eNB or RS is insufficient tosuccessfully decode an entire transmission. In joint decoding, multipleeNBs or RSs may partially decode a portion of the transmission and thenpool or share their partial decoding results to successfully decode thetransmission. Moreover, the eNBs or RSs may each transmit a soft powercontrol command indicating a proportion of power needed to fully decodethe data it estimates as having received. WTRU 110 may then compute thefollowing composite pathloss estimate (PL):

$\begin{matrix}{{P\; L} = {\sum\limits_{i}{\lambda_{i}P\; L_{i}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where λ_(i) represents the proportion of power each eNB or RS needs todecode the data. Variable λ_(i) may also be any value between 0 and 1predetermined by an eNB or RS controlling node or provided by higherlayer. PL_(i) denotes the downlink measurement, i.e., long-termvariation, between WTRU 110 and each eNB or RS.

When λ_(i)=1/K, where K is the number of eNBs or RSs associated with theparticular hop, WTRU 110 may compute an averaged long term loss based onthe downlink measurements between itself and several eNBs or RSs.

Alternatively, the composite pathloss estimate PL may be the median ofPL_(i), where the median of pathloss measurements from multiple pointsmeasures the middle value of the PL measurement distribution. In anotheroption, open loop power control may rely on a downlink path lossmeasurement between WTRU 110 and a reference, primary, or serving eNB orRS having the smallest pathloss estimate.

Again referring to closed loop power control, WTRU 110 may receivemultiple power control commands for one power control loop and produce adecision regarding the transmit power. Any power changes may apply tosome directly controlled channel, such as the dedicated physical controlchannel (DPCCH) in the uplink for HSPA.

Moreover, power of other channels may be set based on grants, signaledoffsets, or the like. One possibility, as employed on soft-handoversituations, may be to increase power if most of the commands request apower increase. This may often be “softened” by including reliabilityinformation about the quality of reception of each command so thaterrors are reduced. Such an approach may apply in soft handover where apower down command from any station means that at least one eNBs or RSsmay be receiving the data adequately well, and the overall power shouldbe reduced to limit interference.

Because distributed communication systems may perform a partialindependent reception followed by coordinated reception, a softerapproach to power control may be desired. For example, each eNB or RSmay send a soft power control command to WTRU 110 that may indicate whatproportion of power may be needed to fully decode the data it estimatesas having received. The power control command may also double as a typeof a soft acknowledge indicator. WTRU 110 may be configured to combinethe soft power control commands and adjust its power to assure thatsufficient, or strong, power is transmitted such that the coordinatingnodes together may receive the full power, but that the total power doesnot exceed the minimum necessary amount by more than a pre-defineddelta.

In one embodiment of the foregoing application variable p_(i) may be thepower control indicator for the i^(th) power control loop, where p_(i)may be a quantized soft value in the range 0 to 1. WTRU 110 may beconfigured to compute total power

$p_{T} = {\sum\limits_{i}{p_{i}.}}$

WTRU 110 may then power up if p_(T)<1, power down if p_(T)>1+Δ, or makeno power changes.

A primary transmit power control (TPC) command may be sent from aprimary or master eNB or RS that collects the quality of reception fromall the coordinating eNBs or RSs to determine whether the transmit powerneeds to be increased or decreased. For this case, it is assumed thatthe coordinating RSs share their reception quality with the primarynode. The primary or master eNB or RS may be the same node that WTRU 110uses for a downlink reference pathloss measurement for an open loopoperation.

Referring again to FIG. 2, in the case that RS assistance is necessarydifferent uplink scenarios of WTRU 110 may occur in a RS enhanced cell.In a direct communication configuration, sometimes referred to as aone-hop configuration, the WTRU 110 to eNB 120 link is good and there isno need for the assistance from a RS 115. For this case, the WTRU 110transmit power is controlled by the TPC issued by eNB 120. WTRU 110 isconnected to eNB 120 and power control may be open loop or closed loop.WTRU 110 may compensate for the long-term channel variations between eNB120 and WTRU 110 and adjust transmission power whenever a TPC message isprovided from eNB 120.

In a simple forwarding configuration, the direct link between WTRU 110and eNB 120 may be poor and cannot sustain direct communications. Inthis case the WTRU 110 is connected to RS 115. In the one RS TPC at WTRUcase, the link between WTRU 110 and one RS 115 is better than otherconnected links, and the RS 115 may be referred to as the Primary RS(PRS). Any other connected RSs to the WTRU 110 are secondary RSs. WTRU110 transmit power may be controlled by the TPC commands issued by thePRS in multiple relay cases or one RS in a single relay case. For themultiple RSs TPC at the WTRU case, multiple relays have equally goodchannel qualities to WTRU 110, the WTRU transmit power may be controlledjointly by multiple RSs.

In a triangle communication configuration, the direct link between WTRU110 and eNB 120 is present, but insufficient to achieve optimalcommunications such that the RS's help may be needed. The trianglecommunication, denoting a communication path from WTRU to RS to WTRU,may lead to different distributed communication relaying schemes, suchas multicast forwarding relaying, simple cooperative relaying, multicastcooperative relaying, or the like.

In an opportunistic cooperation configuration with a primary RS (PRS),the PRS has a sufficient connection to WTRU 110 and the links betweenWTRU 110 and other secondary RSs or eNBs are weak. For this case theprimary connection between the WTRU 110 and an eNB is via the PRS, withthe connection between WTRU 110 and the other secondary RSs or eNBsproviding opportunistic assistance to the primary communication path. Inthis configuration, the WTRU to PRS and PRS to eNB links may be treatedas the primary links with the WTRU to eNB or WTRU to secondary RS linksproviding opportunistic assistance to the communication along theprimary links. As such, WTRU 110 transmit power may be controlled by theTPC messages issued by the PRS, which is referred to as one RS TPC atWTRU.

In an opportunistic cooperation configuration with multiple RSs, thelinks between WTRU 110 to multiple RSs may be equally better than thelink between WTRU 110 and an eNB. WTRU 110 transmit power may becontrolled jointly by the TPC commands issued by multiple RS's, whichmay be referred to multiple RSs TPC at WTRU.

In a strong cooperation configuration, the direct link between WTRU 110and eNB 120 may be reasonable although insufficient to sustain directcommunication and WTRU 110 may communicate with eNB 120 using parallelcommunication paths, namely the direct WTRU to eNB path as well as WTRUto RS to BS path via RS 115. In this configuration, there is nodistinction among various links as they are all treated equally. Assuch, WTRU 110 transmit power may be controlled jointly by the TPCcommands issued by RS 115 as well as eNB 120, also referred to as jointRS & BS TPC at the WTRU.

In FIG. 2, when RS 115 is present the uplink communication between WTRU110 and eNB 120 may occur in M phases. For instance, when M=2 differentscenarios may exist. During phase 1, RS 115 may receive transmissionsfrom WTRU 110. When multicast is not enabled, (e.g, simple forwardingrelaying, cooperative delaying and etc.), eNB 120 does not receive anysignals directly from WTRU 110 during phase 1. For the case thatmulticast is enabled, (e.g., multicast forwarding, multicast cooperativerelaying and etc.), eNB 120 may be configured to receive signalsdirectly from WTRU 110 in phase 1.

Still referring to FIG. 2, during phase 2 RS 115 may transmit to eNB120. For the case that cooperation is not enabled, (e.g, simpleforwarding, multicast forwarding), WTRU 110 does not transmit the datato the eNB 120 during phase 2. In this case, WTRU 110 may remain in idlemode and no power control may be needed for WTRU 110.

For the case that cooperation is enabled, (e.g., cooperative relaying,multicast cooperative relaying), WTRU 110 may send data to eNB 120 inphase 2, and thus WTRU 110 and RS 115 may employ distributedcommunication schemes, (e.g., spatial diversity schemes or spatialmultiplexing), to improve the throughput at eNB 120. For example, theopportunistic cooperation configuration with PRS or multiple RSs mayimplement a loosely synchronized diversity transmission of the RSsignal. Alternatively, the strong cooperation configuration mayimplement tightly synchronized distributed MIMO schemes, such asspace-time diversity codes or distributed spatial multiplexingtransmission schemes.

FIGS. 3( a) and 3(b) provide examples of uplink power control for thesimple forwarding transmission configuration where the number of RSs Nis 3. In the simple forwarding configuration, WTRU 110 is connected to NRSs, where N is larger or equal to one. FIG. 3( a) is an example withone RS TPC. FIG. 3( b) is an example with multiple RSs TPCs.

In FIG. 3( a), RS 304 may be the primary RS (PRS). Based on the downlinkmeasurement between RS 304 and WTRU 308, WTRU 308 may be configured tocompensate for the long-term variations and perform open loop powercontrol for RSs 302, 304, and 306. WTRU 308 responds to TPC command 312from RS 304 to adjust transmit power to perform closed loop powercontrol.

FIG. 4 shows an example of a response to multiple TPC commands from NRSs, where N=2. In the case of multiple RSs TPCs shown in FIG. 3( b),the open loop power control of WTRU 324 may be configured to adjust thetransmit power based on the multiple downlink information used by theWTRU 324 to calculate a “mixture” long-term loss that were sent from RSs318, 320, and 322. For closed loop power control, WTRU 324 may beconfigured to adjust transmission power based on 330 and 336 commandssent from multiple controlling RSs 320 and 322 shown in 402 and 404,respectively. Commands 402 and 404 may be sent for each transmissiontime interval (TTI), as desired. Accordingly, WTRU 324 may be configuredto derive a coordinated combined TPC command 406.

In order to minimize the inter-cell interference, WTRU 324 may beconfigured to increase the transmit power if all of RSs 318, 320, and322 signal an up command. WTRU 324 may then transmit the minimum powerdesired by all RS 318, 320, and 322. WTRU 324 may also decrease thetransmit power if any one of commands 328, 330, and 336 signals a DOWNcommand.

FIG. 5( a) shows an example of coordinated power control where multipleRSs 502, 504, and 506 may coordinate and send one or reduced number ofpower control commands in the downlink. In FIG. 5( a) although three RSsare shown the number of RSs may be any number greater than 1. One of RSs502, 504, and 506 may be selected a-priori to be a master RS. Forexample, the selection may be performed as part of RS selection or RSreselection procedure. The selected RS may change in time, as WTRU 508moves thereby changing the RSs that are visible or as thecommunication-state (e.g. load) of RSs changes in time. For the presentexample, RS 504 is the master RS.

Each RS 502, 504, and 506 may estimate a channel quality indicator (CQI)for each of the various WTRU 508 uplink channels. For example, WTRU 508may be configured to transmit a reference signal, that RSs 502, 504, and506 process to estimate the CQI for that channel. Alternately, the CQImay also be estimated using data driven algorithms, based on decisionfeedback techniques. The CQI measurements may be performed at regulartime intervals.

RS 502 and 506 may be configured to report CQI measurements to Master RS504 using inter-relay links. CQI measurement reports may include anRS-specific ID, and transmitted using a part of the eNB to RS to WTRUradio channels or using out-of-band signaling.

Master RS 504 may be configured to process the various CQI measurementreports 503 and 505, including its own measurement and determine theoptimal power setting for WTRU 508. This may be converted into atransmit power control command 512 that is transmitted to WTRU 508 inthe downlink. Master RS 504 may also be configured to take into accounta relay-transmission-scheme (e.g. simple-forwarding or cooperativetransmission scheme) and the quality of channels between RSs 502, 504,and 506 and an eNB. If eNB to RS CQIs are also considered, RSs 502 and506 may be configured to transmit their corresponding eNB to RS CQIsalso to Master RS 504, making use of inter-relay links.

Alternatively, in FIG. 5( b) CQI estimated by RS 518, 520, and 522 maybe reported to WTRU 524 using one of the downlink links 528, 532, and536, respectively. WTRU broadcasts these CQI reports in its uplinktransmissions 526, 534, and 538. The broadcast signal is received by allRSs 518, 520, and 522, including the Master RS 520, which determines TPCcommand 530.

If there are two relays involved, WTRU 524 may be configured to use anetwork coding approach, whereby the WTRU 524 sends a modulo-2 summationof CQI 532 and CQI 536. Master RS 520 receives this summation andmodulo-2 subtracts CQI 536. This approach saves resources needed totransmit CQI data 526, 534, and 538.

In yet another alternative the control signals may be split betweenshort and long term. The WTRU uses the short term information sentindependently by RSs without fast coordination. The signals may becombined according to signals sent from BS based on slow information.

Multiple power control loops may be implemented in distributed MIMOschemes where a WTRU is configured to communicate with multiple RSs oreNBs, the RS and WTRU may cooperatively transmit to an eNB, or othersimilar configurations. A separate power control loop may be maintainedfor each distributed MIMO configuration. The separate power control looprefers to a WTRU that may be configured to compensate for the long-termvariations between itself and a target RS or eNB and to respond to apower control feedback, such as a TPC command, provided by a RS or eNBwhen available.

When one-relay hop or a two-phase communication is considered, dualpower control loops may be used. One power control loop may beassociated with the phase in that RS 115 is receiving from WTRU 110 andthe other power control loop may be associated with the phase in that RS115 is transmitting and WTRU 110 is transmitting to the samedestination.

FIGS. 6( a) and 6(b) show an example of uplink power control for anopportunistic cooperation configuration in a two-phase communicationwhen a primary RS 604 exists. In the opportunistic cooperationconfiguration WTRU 608 has sufficient connection quality with at leastone RS 604 but link 603 to eNB 605 is insufficient to sustain a directcommunication. eNB 605 may opportunistically receive data via link 603from WTRU 608 when RSs 602, 604, and 606 are receiving. In phase 1 shownin FIG. 6( a), power control loop 607 is provided between WTRU 608 andprimary RS 604. In phase 2 shown in FIG. 6( b), power control loop 610is provided between WTRU 608 and eNB 605.

FIGS. 7( a) and 7(b) show an example of uplink power control for theopportunistic cooperation configuration with a relaying assistantcommunication when multiple equally good RSs exist. In phase 1 shown in7(a), power control loops 707 are provided between WTRU 708 and RSs 702,704, and 706. In phase 2, power control loop 710 is provided betweenWTRU 708 and eNB 705.

Assuming that one relay hop is considered, the power control loop inphase 1 is similar to the one shown in FIGS. 3( a) and 3(b). In phase 2,the transmission target of WTRU 608 or 708 may change from one or moreRSs to eNB 605 or 705, respectively. The initial power setting of theWTRU in each phase may depend on the transmission target for thedifferent phases. The changing of initial power settings in differentphases may be based on the existing signaling, such as an ACK from a RSor extra signaling provided by the primary RS or higher layer.

The opportunistic cooperation configuration in FIGS. 6( a), 6(b), 7(a),and 7(b) may allow for simple control and reduced signaling overheadfrom eNBs 605 and 705. However, it may also provide reduced potentialmulticast benefit if multicast option is used, that is if the eNB 605and 705 opportunistically receives phase 1 transmissions from WTRUs 608and 708, respectively.

FIGS. 8( a) and 8(b) show an example of uplink power control for astrong cooperation configuration in a two-phase communication whenmultiple equally good RSs exist. In the strong cooperation configurationthe direct link between the WTRU 808 and eNB 810 is reasonable althoughinsufficient to sustain direct communication. WTRU 808 communicates withthe eNB 810 using parallel communication paths, namely the direct WTRUto eNB path as well as a WTRU to RS to eNB path via the RSs.

In phase 1 shown in FIG. 8( a), power control loops 807 and 811 areprovided between WTRU 808 to eNB 810 and RSs 802, 804, and 806. In phase2 shown in FIG. 8( b), power control loop 813 is provided between WTRU808 and eNB 810.

Open loop power control in phase 1 of WTRU 808 may be configured tocalculate a mixture value to compensate for the long-term channelvariations between itself and eNB 810 or RSs 802, 804, and 806. Thismixture, for example, may be a combined value of downlink pathloss andshadowing estimates.

For closed loop power control, joint RS and eNB TPC reception may beenabled in phase 1 as shown in FIG. 8( c). WTRU 808 may derive acombined TPC command 816 based on the multiple power control TPCcommands issued by multiple RSs via power control loops 811 shown in 814and the TPC command issued by the eNB via power control loop 807 shownin 812. Commands 812 and 814 may be sent for each transmission timeinterval (TTI), as desired. Alternatively, WTRU 808 may be configured toincrease transmit power if both RSs 802, 804, and 806 and eNB 810 signalan UP command. WTRU 808 may transmit the minimum power desired by theRSs and eNB. WTRU 808 may be further configured to decrease transmitpower if either RSs 802, 804, and 806 or eNB 810 signal a DOWN command.

In phase 2, the transmission of WTRU 808 may be changed to eNB 810. WTRU808 may then be configured to compensate for the long-term channel lossbetween eNB 810 and WTRU 808. For closed loop power control, WTRU 808may be configured to respond to eNB 810 TPCs via power control loop 813to adjust transmit power.

As discussed, different from multiple power control loops another optioncomprises the use of one power control loop among different phases forWTRU 110 power adjustment. Having one power control loop may not meanthat the transmit power is maintained among different phases. One powerloop refers to a single controlling node to control the transmit powerof WTRU 110. For example, in a two-phase transmission, the transmitpower difference between phase 1 and phase 2 may be pre-determined,which may be signaled by the eNB 120 or provided by higher layersignaling. In phase 1, WTRU 110 may be configured to set up the transmitpower based on the pathloss estimate between RS 115 and itself. If WTRU110 transmits in phase 2, the power offset between phase 1 and phase 2may be signaled by eNB 120 or provided higher layer such as by a radioresource control (RRC) communication.

In another embodiment, it is desirable to transmit uplink packets at thehighest possible rate for applications such as higher quality videoconferencing, photo uploads, or the like. By employing higher transmitpower, a link may be established with a higher modulation and codingscheme (MCS) thereby allowing a higher throughput. While WTRU 110 and RS115 transmit power is higher, the packets require less time to transmitreducing the power penalty for such an operation.

For either WTRUs in phase 1 or RSs in phase 2, WTRU 110 may beconfigured to increase transmit power if any controlling RSs 115 signalan UP command. WTRU 110 may transmit the minimum power desired by allRSs 115. WTRU 110 may further be configured to decrease transmit powerif all the RSs 115 signal a DOWN command. All connected RSs 115 may thenincrease their transmit power if they receive an UP command from eNB120. All connected RSs 115 may decrease their transmit power if theyreceive a DOWN command from eNB 120.

Increased transmit power from the WTRUs or RSs may increase the amountof intra-cell or inter-cell interference for CDMA and HSPA basednetworks. However, intra-cell interference is negligible due to theorthogonal nature of OFDM communications and assuming that RSs within acell are time synchronized. Inter-cell interference may be problematicfor all types of networks.

For networks with centralized scheduling, there exists an opportunity toreduce inter-cell interference through the use of dynamic channelallocation (DCA). In order to reduce inter-cell interference, WTRUs orRSs from adjacent cells should not use the same subcarriers. Subcarriersmay be allocated according a variety of well known DCA algorithms.Fractional frequency reuse may also be employed. Therefore, the DCA isapplied to the “outer ring” or cell edge region of a cell. This mayallow for coordination to reduce inter-cell-interference and improvecell-edge performance.

Alternatively, neighboring cells may communicate, such as through X2signaling in LTE, to identify which resource blocks (RBs) are assignedto the WTRUs with high power such that collisions may be avoided.Alternatively, a predetermined number of RBs may be selected andassigned to a high power WTRU. Once the RBs are loaded, no otherneighboring WTRUs may be assigned to these RBs.

FIG. 9 shows an example of a MIMO network having a flat topology. EacheNB 902 and 904 may be configured to forward power control commands 908and 914 and system information directly to WTRU 906. WTRU 906 may thenintegrate the commands and system information using any of the methodsdiscussed above.

FIG. 10 is a flow diagram of a process in accordance with the presentdescription. If an eNB to WTRU link is sufficient (1000), the WTRU isconfigured to receive TPC commands from the eNB (1002). Otherwise, RSassistance may be needed (1004). The WTRU may then be configured tocommunicate with multiple RSs (1006) such as in a distributedcommunication system. If the WTRU communicates with one RS, a TPCcommand may be received from one RS (1008) and the WTRU may beconfigured for opportunistic cooperation, as previously described, withany eNBs or RSs (1010) such as in a distributed communication system. Ifthe WTRU has sufficient link quality with multiple RSs (1012), the WTRUmay be configured to receive and combine TPC commands from multiple RSs(1018). Otherwise, the WTRU may receive a TPC command from a master orprimary RS (1014) and the WTRU may be configured for opportunisticcooperation with any eNBs or RSs (1016) such as in a distributedcommunication system.

FIG. 11 is a flow diagram of another process in accordance with thepresent description. A WTRU may be configured for opportunisticcooperation, as previously described, with one or more RSs and receiveTPC commands from one or more RSs or eNBs in phase 1 (1102). The WTRUmay also be configured for opportunistic cooperation with an eNB inphase 1 (1104). The WTRU may be configured to receive a TPC command froman eNB in phase 2 (1106). The WTRU may configured for opportunisticcooperation with one or more RSs in phase 2 (1108).

Although features and elements are described above in particularcombinations, each feature or element may be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs),Application Specific Standard Products (ASSPs); Field Programmable GateArrays (FPGAs) circuits, any other type of integrated circuit (IC),and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, Mobility ManagementEntity (MME) or Evolved Packet Core (EPC), or any host computer. TheWTRU may be used in conjunction with modules, implemented in hardwareand/or software including a Software Defined Radio (SDR), and othercomponents such as a camera, a video camera module, a videophone, aspeakerphone, a vibration device, a speaker, a microphone, a televisiontransceiver, a hands free headset, a keyboard, a Bluetooth® module, afrequency modulated (FM) radio unit, a Near Field Communication (NFC)Module, a liquid crystal display (LCD) display unit, an organiclight-emitting diode (OLED) display unit, a digital music player, amedia player, a video game player module, an Internet browser, and/orany Wireless Local Area Network (WLAN) or Ultra Wide Band (UWB) module.

1. A method for power control in a wireless transmit/receive unit (WTRU)configured for distributed communications, the method comprising:communicating concurrently by the WTRU via one or more transceivers withtwo or more base stations and one or more relay stations (RSs);maintaining two or more closed loop independent power control loops bythe WTRU with the two or more base stations and the one or more RSs; andreceiving different transmit power control (TPC) commands by the WTRUfrom each of the two or more closed loop independent power control loopsduring two or more time intervals.
 2. The method of claim 1 furthercomprising determining a primary RS from the one or more RSs, andreceiving by the WTRU a primary TPC command from the primary RS whilecommunicating concurrently with the one or more RSs.
 3. The method ofclaim 2 wherein the primary TPC command from the primary RS is acoordinated combined TPC command.
 4. The method of claim 1 furthercomprising transmitting by the WTRU the received different TPC commandsto the one or more RSs.
 5. The method of claim 1 further comprisingcombining by the WTRU the received different TPC commands anddetermining by the WTRU a transmit power increase or decrease bycombining the received different TPC commands.
 6. The method of claim 1wherein the distributed communications is configured for multi-usermultiple in/multiple out (MIMO) communications.
 7. The method of claim 1wherein the distributed communications is configured for Long TermEvolution (LTE), 802.16, High Speed Packet Access (HSPA), or codedivision multiple access (CDMA) communications.
 8. The method of claim 1further comprising computing a path loss by the WTRU for open loop powercontrol based on a proportion of power needed by the two or more basestations and the one or more RSs and path loss estimates between theWTRU and the two or more base stations and the one or more RSs.
 9. Themethod of claim 1 further comprising communicating concurrently by theWTRU with the two or more base stations and the one or more RSs withparallel communication paths.
 10. A wireless transmit/receive unit(WTRU) configured for distributed communications, the WTRU comprising:one or more transceivers configured to communicate concurrently with twoor more base stations and one or more relay stations (RSs); the one ormore transceivers configured to maintain two or more closed loopindependent power control loops with the two or more base stations andthe one or more RSs; and the one or more transceivers configured toreceive different transmit power control (TPC) commands from each of thetwo or more closed loop independent power control loops during two ormore time intervals.
 11. The WTRU of claim 10 further configured todetermine a primary RS from the one or more RSs, and the one or moretransceivers configured to receive a primary TPC command from theprimary RS while communicating concurrently with the one or more RSs.12. The WTRU of claim 11 wherein the primary TPC command from theprimary RS is a coordinated combined TPC command.
 13. The WTRU of claim10 wherein the one or more transceivers are configured to transmit thereceived different TPC commands to the one or more RSs.
 14. The WTRU ofclaim 10 further configured to combine the received different TPCcommands and determine a transmit power increase or decrease bycombining the received different TPC commands.
 15. The WTRU of claim 10wherein the distributed communications is configured for multi-usermultiple in/multiple out (MIMO) communications.
 16. The WTRU of claim 10wherein the distributed communications is configured for Long TermEvolution (LTE), 802.16, High Speed Packet Access (HSPA), or codedivision multiple access (CDMA) communications.
 17. The WTRU of claim 10further configured to compute a path loss for open loop power controlbased on a proportion of power needed by the two or more base stationsand the one or more RSs and path loss estimates between the WTRU and thetwo or more base stations and the one or more RSs.
 18. The WTRU of claim10 further configured to communicate concurrently with the two or morebase stations and the one or more RSs with parallel communication paths.